Methods, devices, and systems for improved oxygenation patient monitoring, mixing, and delivery

ABSTRACT

A computer implemented method is disclosed for providing adaptive control of a gas mixture for delivery to a patient via a separate external gas blender system. The computer implemented method includes receiving first SpO 2  data from a regional oximeter via a regional oximeter interface; determining first PaO 2  data using a first lookup table derived from a first sigmoid shaped oxyhemoglobin dissociation curve; determining a first gas mixture value using the first PaO 2  data; and transmitting first adaptive feedback control data including the first gas mixture value to the separate external gas blender system via a gas blender interface.

TECHNICAL FIELD

The present invention relates generally to medical devices, and morespecifically, oxygenation monitoring, mixing, and delivery to patients.

COPYRIGHT AND TRADEMARK INFORMATION

A portion of the disclosure of this patent document contains materialwhich is subject to copyright protection. The copyright owner has noobjection to the facsimile reproduction of the patent document or thepatent disclosure, as it appears in the Patent and Trademark Officepatent file or records, but otherwise reserves all copyright rightswhatsoever. Trademarks are the property of their respective owners.

BACKGROUND

Oxygen mixing and delivery systems are used to blend concentrated oxygenwith ambient air and/or other gasses in order to provide for delivery(infusion) of the blended gasses to a patient to assist in breathing.Such systems may utilize invasive delivery to the patient for example byuse of endotracheal tubes, or may provide delivery of the gasses in anon-invasive manner such as by use of a cannula or mask. Recent researchand patient studies have shown significant value in certain patients formonitoring and adjusting oxygen levels of the brain and other tissues.Specifically, regional oximetry provides consistent and accuratemonitoring of oxygen saturation within tissues and the brain. Pulseoximetry does not provide reliable data making it difficult to determineacceptable oxygenation levels in these areas of the patient. Withoutregional oximetry, conditions where cerebral tissue becomes underoxygenated (i.e hypoxemia) or over oxygenated (i.e. hyperoxia) can putpatients at risk. Cerebral tissue hypoxia may cause brain damage or evendeath and is of major concern to anesthesiologists during surgery.Supplemental oxygen is necessary for preterm infants due to lungimmaturity. However, over oxygenation resulting in hyperoxia may lead tooxidative stress in these newborns. Oxidative stress occurs when thereare more toxic free radicals produced than can be neutralized byantioxidant mechanisms, Oxidative stress can lead to red blood cellinjuries, lung, retina, central nervous system, and possibly generalizedtissue damage.

Improved methods, devices, and systems for regulating the blending ofconcentrated oxygen with ambient air and/or other gasses are needed forpatients undergoing regional oximetry.

SUMMARY

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used to limit the scope of the claimed subject matter.

In one embodiment, a computer implemented method is disclosed forproviding adaptive control of a gas mixture for delivery to a patientvia a separate external gas blender system. The computer implementedmethod includes receiving first SpO₂ data from a regional oximeter via aregional oximeter interface; determining first PaO₂ data using a firstlookup table derived from a first sigmoid shaped oxyhemoglobindissociation curve; determining a first gas mixture value using thefirst PaO₂ data; and transmitting first adaptive feedback control dataincluding the first gas mixture value to the separate external gasblender system via a gas blender interface.

In some embodiments, the computer implemented method may further includereceiving second SpO2 data from a pulse oximeter via a pulse oximeterinterface. In certain embodiments, the computer implemented method mayinclude determining second PaO2 data using a second lookup table derivedfrom a second sigmoid shaped oxyhemoglobin dissociation curve. In otherembodiments, the computer implemented method may include determining asecond gas mixture value using the second PaO2 data. In furtherembodiments, the computer implemented method may include, uponactivation of a software switch, transmitting second adaptive feedbackcontrol data including the second gas mixture value to the separateexternal gas blender system via the gas blender interface.

In some embodiments, the activation of the software switch may be acontrolled by a user interface. The activation of the software switchmay also be controlled by detecting invalid data or missing data fromthe regional oximeter interface.

In certain embodiments, the computer implemented method may furtherinclude transmitting at least a portion of the first SpO₂ data and atleast a portion of the second SpO₂ data to the user interface, and,optionally, transmitting at least a portion of the first PaO₂ data andat least a portion of the second PaO₂ data to the user interface. Incertain embodiments, the regional oximeter may be a regional cerebraloxygen saturation monitor.

The computer implemented method may further include converting a firstSpO₂ value from the first SpO₂ data to a first PaO₂ value usinginterpolation upon determining the first SpO₂ value is not present inthe first lookup table. Determining the first gas mixture value usingthe first PaO₂ data may include determining a weighted average of afirst sample period and a second sample period. The second sample periodmay occur immediately after the first sample period. The weightedaverage may be approximately 90% for the first sample period and may beapproximately 10% for the second sample period of the first PaO₂ data.

In another embodiment, a computing device for providing adaptive controlof a gas mixture for delivery to a patient via a separate external gasblender system is disclosed. The computer device includes a memory; andat least one processor configured to perform a method. The methodincludes receiving first SpO₂ data from a regional oximeter via aregional oximeter interface; determining first PaO₂ data using a firstlookup table derived from a first sigmoid shaped oxyhemoglobindissociation curve; determining a first gas mixture value using thefirst PaO₂ data; and transmitting first adaptive feedback control dataincluding the first gas mixture value to the separate external gasblender system via a gas blender interface.

In some embodiments, the method may further include receiving secondSpO2 data from a pulse oximeter via a pulse oximeter interface. Incertain embodiments, the method may include determining second PaO2 datausing a second lookup table derived from a second sigmoid shapedoxyhemoglobin dissociation curve. In other embodiments, the method mayinclude determining a second gas mixture value using the second PaO2data. In further embodiments, the method may include, upon activation ofa software switch, transmitting second adaptive feedback control dataincluding the second gas mixture value to the separate external gasblender system via the gas blender interface.

In some embodiments, the activation of the software switch is controlledby a user interface. The activation of the software switch may also becontrolled by detecting invalid data or missing data from the regionaloximeter interface. The method may further include transmitting at leasta portion of the first SpO₂ data and at least a portion of the secondSpO₂ data to the user interface, transmitting at least a portion of thefirst PaO₂ data and at least a portion of the second PaO₂ data to theuser interface. In certain embodiments, the regional oximeter is aregional cerebral oxygen saturation monitor.

The method may further include converting a first SpO₂ value from thefirst SpO₂ data to a first PaO₂ value using interpolation upondetermining the first SpO₂ value is not present in the first lookuptable. Determining the first gas mixture value using the first PaO₂ datamay include determining a weighted average of a first sample period anda second sample period. The second sample period may occur immediatelyafter the first sample period. The weighted average may be approximately90% for the first sample period and may be approximately 10% for thesecond sample period of the first PaO₂ data.

In another embodiment, a non-transitory computer-readable storagemedium, storing one or more programs for execution by one or moreprocessors of a computing device, the one or more programs includinginstructions for receiving first SpO₂ data from a regional oximeter viaa regional oximeter interface; determining first PaO₂ data using a firstlookup table derived from a first sigmoid shaped oxyhemoglobindissociation curve; determining a first gas mixture value using thefirst PaO₂ data; and transmitting first adaptive feedback control dataincluding the first gas mixture value to the separate external gasblender system via a gas blender interface.

In some embodiments, the method further includes receiving second SpO₂data from a pulse oximeter via a pulse oximeter interface, determiningsecond PaO₂ data using a second lookup table derived from a secondsigmoid shaped oxyhemoglobin dissociation curve, determining a secondgas mixture value using the second PaO₂ data, and upon activation of asoftware switch, transmitting second adaptive feedback control dataincluding the second gas mixture value to the separate external gasblender system via the gas blender interface.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary, as well as the following detailed description ofpreferred embodiments, is better understood when read in conjunctionwith the appended drawings. For the purposes of illustration, there isshown in the drawings exemplary embodiments; however, the presentlydisclosed invention is not limited to the specific methods andinstrumentalities disclosed. In the drawings:

FIG. 1 is a block diagram of an example of an oxygen mixing and deliverysystem using a pulse oximeter in accordance with embodiments of thepresent disclosure.

FIG. 2 is a more detailed block diagram of an example of an oxygenmixing and delivery system in accordance with embodiments of the presentdisclosure.

FIG. 3 is a block diagram of an example PID controller system inaccordance with embodiments of the present disclosure.

FIG. 4 is a graph depicting an approximation of an oxyhemoglobindissociation curve in accordance with embodiments of the presentdisclosure.

FIG. 5 is an example flow chart of overall operation of an illustrativesystem in accordance with embodiments of the present disclosure.

FIGS. 6A through 6I depict a flow chart of an example operationalprocess in accordance with embodiments of the present disclosure.

FIG. 7 is a flow chart of an example set of alarm operations inaccordance with embodiments of the present disclosure.

FIG. 8 is another more detailed block diagram of an example of an oxygenmixing and delivery system in accordance with embodiments of the presentdisclosure.

GLOSSARY

Reference throughout this document to “one embodiment”, “certain exampleembodiments”, “examples”, “an embodiment”, “an example”, “animplementation” or similar terms may mean that a particular feature,structure, or characteristic described in connection with theembodiment, example or implementation is included in at least oneembodiment, example or implementation of the present invention. Thus,the appearances of such phrases or in various places throughout thisspecification may not necessarily all refer to the same embodiment,example or implementation. Furthermore, the particular features,structures, or characteristics may be combined in any suitable manner inone or more embodiments, examples or implementations without limitation.

The term “or” as used herein is to be interpreted as an inclusive ormeaning any one or any combination. Therefore, “A, B or C” means “any ofthe following: A; B; C; A and B; A and C; B and C; A, B and C”. Anexception to this definition will occur only when a combination ofelements, functions, steps or acts are in some way inherently mutuallyexclusive.

The terms “a” or “an”, as used herein, are defined as one or more thanone. The term “plurality”, as used herein, is defined as two or morethan two. The term “another”, as used herein, is defined as at least asecond or more. The terms “including” and/or “having”, as used herein,are defined as comprising (i.e., open language). The term “about” or“approximately”, as used herein in relation to a stated value, should betaken to mean any value within ±20% of the stated value.

The term “coupled”, as used herein, is defined as connected, althoughnot necessarily directly, and not necessarily mechanically.

The term “program” or “computer program” or similar terms, as usedherein, is defined as a sequence of instructions designed for executionon a computer system. A “program”, or “computer program”, may include asubroutine, a function, a procedure, an object method, an objectimplementation, in an executable application, an app, a widget, anapplet, a servlet, a source code, an object code, a sketch, a sharedlibrary/dynamic load library and/or other sequence of instructionsdesigned for execution on a computer system.

The term “processor”, “controller”, “CPU”, “Computer” and the like asused herein may encompass both hard programmed, special purpose, generalpurpose and programmable devices and may encompass a plurality of suchdevices or a single device in either a distributed or centralizedconfiguration without limitation.

The term “SpO₂” is an acronym for “Saturation of Peripheral Oxygen”.Within the related technology, the term SpO₂ may often casually bereferred to as “blood oxygen”, “blood oxygen saturation”, “blood oxygenconcentration” and other similar terms. While any suitable measurementof “oxygen saturation” can be used in a manner consistent withApplicant's teachings herein, one implementation uses SpO₂. SpO₂ may beused as an estimation of blood oxygen concentration and is usuallymeasured with a pulse oximeter.

The term “solenoid valve” or simply “solenoid” means a valve device thatis used to control two or more gasses from two or more inputs to directthe gasses to a single output.

The term “bi-modal solenoid valve” or simply “bi-modal solenoid” means atype of solenoid valve device which allows only one gas from one of itsinputs to be directed to a single output based upon control signals. Forexample, the proportion of mixture of two gasses can be controlled bycontrolling the amount of time each input is directed to the output.

The term “proportional solenoid valve” or simply “proportional solenoid”is used to refer to a type of solenoid valve device in which two or moregasses from two or more inputs can be controlled in a manner that allowseach input to be directed to the output proportionally so that, forexample, one input may be set to 30% of full flow while the other inputmay be set to 70% full flow. This proportionality can be controlledeither by signals that cause the valves to open and close in proportionto one another, or by signals that individually select the degree towhich each valve is open or closed.

The term “invasive” is used to describe the delivery of gasses to apatient by use of an endotracheal tube or the like.

The term “non-invasive” is used to describe delivery of gasses to apatient by use of a mask or cannula or the like.

A “pulse oximeter” is a photoelectric device that measures the amount ofsaturated hemoglobin in the tissue capillaries by transmitting beams oflight through the tissue to a light receiver. A pulse oximeter maygenerally be configured so as to clip or otherwise attach onto afingertip or earlobe, or other suitable location. The amount ofsaturated hemoglobin affects the wavelength and reflection ortransmission of the light transmitted through the tissue. By analyzingthe received light, a percentage of oxygen saturation (SpO₂) of theblood can be deduced. Commercially available pulse oximeters may alsoprovide for measurement of a pulse as well as generating various alarmcondition signals.

A “regional oximeter” is designed for cerebral tissue monitoring ofoxygen saturation (SpO₂) of the blood to prevent cerebral hypoxia. Thesedevices allow accurate measurements of tissue oxygen saturation of atrisk patients that may have compromised oxygen saturation to the brain.These devices may be suitable for adult, pediatric, and neonatalpatients. Patients may be monitored in hospitals, long-term carefacilities, sleep laboratories, sub-acute care facilities, etc. Anear-infrared light spectrum or other suitable spectrum is used by theregional oximeter to penetrate tissue (including muscle and bone). Thesensors are positioned at fixed distances from a light emitter.Specifically, adhesive pads attach the sensors and light meter to thepatient's scalp. Specialized algorithms subtract superficial lightabsorptions from deep tissue light absorption to determine the tissueoxygenation levels. By utilizing two photodetectors with each lightsource, the regional oximeter can provide selective sampling of tissueat a specified depth beneath the skin. To accomplish this, the regionaloximeter subtracts near-field photo detection from far-fieldphoto-detection. This is an example of providing selective tissueoxygenation measurement to pre-defined depths within the patient.

The term “smart” is intended to designate an operational mode in whichthe oxygen delivery rate is adaptively feedback controlled as opposed tomanual control.

The term “PaO₂” means partial pressure of arterial oxygen.

The term “FiO₂” means fraction of inspired oxygen and in this discussionrepresents a blend of gas delivered to the patient.

The term “button” is used to mean a switch that makes a user selectionin a user interface and may be realized as an electromechanical switchor as a virtual button displayed on, e.g., a touchscreen display.

A proportional-integral-derivative controller (PID controller) is acontrol loop feedback controller. A PID controller calculates an errorvalue as the difference between a measured process variable and adesired value of the process variable (or set point). The controlleroperates to minimize the difference between the measured value and theset point. A PID controller accomplishes this by use of an algorithmthat uses three separate parameters—proportional (P), integral (I) andderivative (D) values interpreted at discrete increments of time where Pdepends on the current error, I depends of the accumulation of pasterrors, and D predicts future errors. The weighted sum of these threeactions may be used to adjust a process—in this case the proportion ofoxygen represented by FiO₂. Mathematically, these values are generallyrepresented by the following equations:

$\begin{matrix}{P = {K_{p}{e(t)}}} & \left( {{Equation}.\mspace{14mu} 1} \right) \\{I = {K_{i}{\int_{0}^{t}{{e(\tau)}d\;\tau}}}} & \left( {{Equation}.\mspace{14mu} 2} \right) \\{D = {K_{d}\frac{{de}(t)}{dt}}} & \left( {{Equation}.\mspace{14mu} 3} \right)\end{matrix}$

where the oxygen mixer control signal is derived from the PID controlleroutput u_(t):

$\begin{matrix}{u_{t} = {{P + I + D} = {{K_{p}{e(t)}} + {K_{i}{\int_{0}^{t}{{e(t)}{dt}}}} + {K_{d}\frac{{de}(t)}{dt}}}}} & \left( {{Equation}.\mspace{14mu} 4} \right)\end{matrix}$

and where:

K_(P: Proportional gain coefficient;)

K_(i: Integral gain coefficient;)

K_(d: Derivative gain coefficient;)

: Error, difference between measured and target;

t: Time; and

: Integration variable; takes on values from time 0 to present time t.

For purposes of this document, a controller may be referenced as a PIDcontroller for convenience and by way of example, but in practice thecontroller may in fact not use all three of the elements ofProportional, Integral and Derivative control. Use of only one or two ofthe PID control functions is common and use of other feedback controlmechanisms is also within the scope of the present teachings.

DETAILED DESCRIPTION

While the present disclosure is susceptible of embodiment in manydifferent forms, specific embodiments are shown in the drawings and willbe herein described in detail, with the understanding that the presentdisclosure of such embodiments is to be considered as an example of theprinciples and not intended to limit the invention to the specificembodiments shown and described. In the description below, likereference numerals are used to describe the same, similar orcorresponding parts in the several views of the drawings.

In accord with certain example embodiments consistent with the presentdisclosure, a gas blending system is provided in which a gas isdelivered to a patient. The gas is usually a mixture of oxygen and air(and/or other gasses) to achieve a desired percentage of oxygen in themixture. In certain embodiments, the gas blending system also providesfor heating and humidification of the gas mixture and measurements ofthe heat and humidity of the supplied gas mixture. A feedback mechanismmay be provided in which the gas blending system provides data toseparate adaptive controller system including data relating to the gasmix, gas temperature, flow rate, humidity etc. In one embodiment, datafrom a pulse oximeter attached to the patient provides data to theadaptive control system such that the adaptive control system cancontrol the percentage of oxygen delivered to the patient via theblender system in order to achieve a target SpO₂ level. Some suchmethods, devices, and systems are disclosed in U.S. Pat. No. 10,007,238titled OXYGEN MIXING AND DELIVERY (U.S. application Ser. No. 14/602,392)the contents of which are incorporated by reference herein.

In another embodiment, data from a regional oximeter in addition to datafrom a pulse oximeter is used selectively such that the adaptive controlsystem can control the percentage of oxygen delivered to the patient. Inthis embodiment, the regional pulse oximeter uses two sensorsnon-invasively attached to the scalp or forehead for the non-invasivemeasuring of cerebral blood oxygen saturation. By comparison, thetraditional pulse oximeter uses only one sensor on an appendage of apatient (e.g., fingertip or the foot, or ear lobe). The two devices havecomplimentary applications—while the traditional pulse oximeter measuresthe pulsatile blood oxygen saturation level of the systemic arterialsystem, the regional oximeter solution measures the pulsatile bloodoxygen saturation level of the brain.

Many variations will occur to those skilled in the art uponconsideration of the present teachings.

Turning now to FIG. 1, an illustrative example of an oxygen mixing anddelivery system is depicted in which a patient 10 is to be provided witha gas mixture to treat any number of breathing disorders, or to providefor respiration during surgical procedures, etc. The patient 10 isfitted with a pulse oximeter 14 that measures the blood oxygen level inthe form of a SpO₂ measurement (which is the output that isconventionally provided by a pulse oximeter).

The pulse oximeter acquires the percentage of a patient's arterial bloodoxygen SpO₂ as well as the patient's pulse rate. The SpO₂ and pulse rateacquired from the patient is input to an adaptive controller system 18that is based upon one or more programmed or hardwiredprocessor/controllers for use as a feedback signal for calculating apercentage of oxygen to be delivered to the patient. The adaptivecontroller system 18 can be used with ventilators, continuous flowsystems, oxygen diluters and benders, collectively and individuallyreferred to herein as blender systems.

Commercially available pulse oximeters such as 10 include mechanisms fordetecting not only pulse rate and SpO₂ levels, but most also detect atleast the conditions of: the sensor on or off the patient, the sensorbeing disconnected and low perfusion. Other sensors can detect otherparameters that can be conveyed to the adaptive controller system 18 andcan be used to provide enhanced alarm detection and other operationalparameters.

As illustrated, the pulse oximeter 14 delivers data measured on thepatient 10 to a pulse oximeter processor 22 forming part of the adaptivecontroller system 18. The adaptive controller system may be configuredto accept connection to any number of different commercially availablepulse oximeters, thereby increasing the flexibility of the system. Pulseoximeter processor 22 in turn converts the data into a form bestprocessed by an adaptive controller 26 (e.g. programmed processor/PIDcontroller). Adaptive controller 26 is programmed to operate as deemedappropriate by medical personnel via a user interface 30 forming a partof the system 18 to provide a prescribed amount of a gas mixture to apatient in order to provide therapy. The feedback data from the pulseoximeter 14 may be used by the adaptive controller to control the oxygenconcentration delivered to the patient to achieve a target SpO₂peripheral blood oxygen level. In the implementation depicted, thiscontrol is via a PID controller which may form part of the adaptivecontroller 26.

Adaptive controller 26 communicates with a blender system 34 via a wiredor wireless communication bus 38 using any suitable communicationprotocol. In certain implementations, the protocol can be, for example,a serial bus interface, a parallel bus interface, an Ethernet interface,IEEE 1394 interface, a Universal Serial Interface (USB) or any othersuitable interface including proprietary interfaces. Further, datarelating to the patient's condition and the gas being provided to thepatient can be provided to remote systems for display to personnel whomonitor multiple patients, for example, using additional communicationinterfaces (not shown).

In accord with the present teachings, the blender system 34 is aseparate device that is packaged in a separate housing and which can beproduced by any number of different manufacturers and adapted to receiveadaptive control from the system 18. Generally, the blender system 34can operate as a standalone gas delivery system that is operable undermanual control by medical personnel. By use of separate blender systemand adaptive controller system, multiple blender systems may be deployedand adapted to various specialized usage at reduced cost and complexitywhen adaptive control is not deemed desirable. Thus, in instances whereadaptive control is not deemed suitable by medical personnel, theblender system can be utilized as a standalone manually controlleddevice. This decreases overall cost and a reduced number of adaptivecontroller systems 18 can be utilized where deemed appropriate withoutincreasing the cost of each blender system deployed in a medicaltreatment facility.

In certain example embodiments, the blender system 34 may receivecompressed gasses from an oxygen source 42 that provides approximately100% oxygen and from a source 46 of compressed air containing oxygen atapproximately 21% oxygen. These gasses, and possibly others, can becombined using known techniques such as, for example, the oxygenblending system disclosed in U.S. Pat. No. 5,388,575 titled ADAPTIVECONTROLLER FOR AUTOMATIC VENTILATORS (U.S. application Ser. No.7/950,897), the contents of which are incorporated by reference herein.

In the present example system, the blender system 34 and the adaptivecontroller system 18 are provided as separate units that are containedin separate mechanical housings that are interconnected by a busconnection 38. This enables the blender system 34 to convenientlyoperate under manual override control in order to override amalfunctioning adaptive controller system 18, or alternatively, tooverride the adaptive controller system so as to permit the careprovider to implement emergency measures in critical medical situation.Power may be supplied to the blender system using an AC power source 50coupled to a facility's power infrastructure (e.g., the 120 volt lineavailable in the U.S.) as well as a battery backup to assure continuousdelivery of the gasses to the patient in the event of a power failure(such systems are often referred to as a UPS or Uninterruptable PowerSource). Similarly, a separate AC power source 54 may be coupled to theadaptive controller system 18. By providing these functions as separatedevices, an interface can be provided that allows use of the adaptivecontroller system 18 with a variety of blender and gas delivery systems,potentially from multiple manufacturers. Further, such blender systemsand gas delivery systems can include those that are capable of manualcontrol that can operate standalone for more stable patients that arenot in need of an adaptive controller system to regulate their SpO₂level. Power sources 50 and 54 may be integral to systems 34 and 18respectively.

It is noted that in the system as depicted, certain analog signals areshown to be received by the various processors. It is to be understoodthat analog to digital conversion or digital to analog conversion iscarried out as called for to render the various signals compatible. Thedetails of such conversions are omitted from these illustrations forclarity.

In accord with one example implementation, the system described by wayof example herein can provide control of the gases to provide at leastone of: a gas flow rate (between about 1 and 60 liters/minute (LPM)); ahigh temperature alarm limit with a tracking alarm limit of about ±2.0°C.; a humidity output of greater than about 33 mg H₂O/L at about 37° C.when used in an invasive mode (e.g., by use of an endotracheal tube orthe like); a humidity output of greater than about 10 mg H₂O/L at 37° C.when used in non-invasive mode (e.g., by use of a mask or cannula); andan alarm limit of SpO₂ below about 90%. Some or all of these values maybe assigned by medical personnel.

Referring now to FIG. 2, in accord with certain example implementationsconsistent with the present teachings, a more detailed depiction of anexample system consistent with the present teachings is shown. Theadaptive controller system 18 includes adaptive controller 26 thatincorporates a programmed processor or hard wired processor circuitconfigured to run a proportional-integral-differential (PID) controlprocess (or other suitable feedback control process) that uses the SpO₂as measured by the pulse oximeter 12 and received by the pulse oximeterprocessor 22 via a suitable interface 24 as an input for calculation ofan oxygen concentration percentage (FiO₂) that is to be delivered to thepatient. Interface 24 can be any suitable interface including those thathave been standardized by various manufacturers of pulse oximeters andmay incorporate multiple interfaces for connection to pulse oximetersmade by multiple manufacturers. Processor 26 utilizes non-transitorystorage and memory 28 for storage of data and programming instructions.

The output of the adaptive controller system 18 provides signals to theblender system's controller 60 and may receive further feedbackinformation from controller 60 via bus 38. In one example embodiment,the bus 38 is a conventional serial bus that is coupled betweenprocessor 26 and controller 60 via interface circuits 39 and 41respectively. In certain implementations, a standard EIA/TIA-232-Eserial interface operating at 38400 baud, with no parity bits, 8 databits and 2 stop bits can be used. Other suitable interfaces can also beutilized without limitation.

Blender Controller 60 controls an oxygen mixer device 65 which usessources of approximately 100% oxygen 42 and air (having approximately21% oxygen) 46 to form a blended gas having a desired FiO₂ as calculatedfor administration as an inspired gas to the patient 10. A controlalgorithm that represents the respiratory physiology of the patient isused by the PID controller embodied in processor 26. The oxygen mixerdevice 64 may, for example, utilize a proportional solenoid valve systemor may use a bi-modal solenoid valve system or any other suitable gasmixing arrangement.

The PID controller of 26 calculates the desired FiO₂ to be generated bythe oxygen mixer 64 and controls the oxygen mixer 64 in order to achievethe calculated gas mixture to obtain or maintain a target SpO₂.

User interface 30 can be any suitable mechanism for input/output of usercommands and display of relevant data. In certain example embodiments,the interface 30, under control of processor 26 supports a display rangeof O₂ supplied by the mixer 64 of about 21% to 100%. Further, theinterface 30, under control of the processor 26 supports a display rangefor informing the user of the patient's SpO₂ between at least about 70to 100%, and a pulse rate display of at least about 50 to 200 beats perminute (BPM). In certain embodiments, no state change or behavior changeoccurs when buttons are pressed or other user actions are input if thoseactions or buttons are designated as currently inactive.

In the example shown, oxygen mixer 64 is configured to receive gases ofapproximately 100% oxygen from oxygen source 42 and air havingapproximately 21% oxygen from source 46 (which may be ambient air orpressurized ambient air) to form a blended gas output. The gas blendingmay be accomplished in several ways. In one example, a bi-modal solenoidvalve is used to alternately pass one or more input gas from sources 42and 46 to the output of the solenoid valve (not shown). The output maybe blended in a chamber prior to delivery to the output of the oxygenmixer. In this example implementation, the percentage of oxygen isadjusted by the relative amount of time each of the inputs to thesolenoid valve is coupled to the solenoid output. Thus, the processor 60(either under control of processor 26 or under manual override control)controls the percentage of oxygen at the output of the mixer by togglingbetween each input port to produce a blended gas at the output port ofthe bi-modal solenoid valve. This output can be further mixed in achamber as previously noted.

In another example embodiment, a proportional solenoid valve isconfigured to as to achieve the blending of the gases. In thisembodiment, the proportional solenoid receives oxygen from source 42 andair from source 46. The processor 60 similarly controls the proportionalsolenoid so as to adjust the mixture of gas. In this example, this isdone by controlling a percentage of gas passed from each input of theproportional solenoid valve to the output to produce the blended gas ofdesired percentage oxygen. A mixing chamber may be used or omitted fromthis implementation since the gasses will generally adequately blend inthe proportional solenoid valve and lines to the patient 10.

When supplemental gases are administered to a patient, the gases can beuncomfortably cool—in part due to the expansion of the gases from theirpressurized sources when released to the oxygen mixer 64. Further, themixed gases may be uncomfortably dry causing a drying of the patient'snasal tissues. In order to enhance the comfort to the patient, incertain example implementations the blender system 34 may incorporate aheater 68 that heats the gas mixture from oxygen mixer 64. Similarly,the gas mixture can be humidified by a humidification device 72 (eitheror both).

In this case, as the blended gas is output by the oxygen mixer 64, theblended gas travels through a heating and humidification system made upof heater 68 and humidifier 72. The heating and humidification systemheats and humidifies the respiratory gases delivered via endotrachealtubes, nasal cannula or face mask to adult, pediatric, infant andneonatal patients. The heating device 68 can utilize any heatingmechanism including electrically resistive heating, heated wire heating,Peltier effect heating, etc.

The humidifier 72 can be realized using any suitable humidificationarrangement. In one example embodiment, the humidifier 38 uses ahumidifier cartridge fed by a sterile water reservoir using any suitablevaporization mechanism including ultrasonic vibration or heating tosteam. In other example embodiments, the gasses air can be bubbledthrough a sterile water reservoir to increase the humidity of the gasmixture. Other variations will occur to those skilled in the art uponconsideration of the present teachings.

Humidifier 72 can provide data to the processor 60 indicating the rateat which water is being consumed or other measure of humidity. This canbe correlated with the amount of gas being delivered to determine thelevel of humidification of the gases. In certain exampleimplementations, the processor 60 can control the humidification levelof humidifier 72 using any suitable control mechanism (e.g., blendingwith un-humidified gas mixture, reduction of level of vaporization,etc.) in order to maintain a target water vapor content in the gases.

The temperature of the gases can be measured using a thermistor or otherheat sensing element that is operatively approximately proximal to thepoint of delivery to the patient via temperature measurement device 76that can reside inside the gas delivery tubes at a location close to thepatient to produce temperature data (i.e., a device that measuresresistance of a thermistor and converts the measurement to digitaltemperature data). This temperature data can be provided to theprocessor 60 that uses the measured temperature to adjust the heater 68so as to achieve a target temperature. Such target temperature is mostoften, but not necessarily, about 37° C.±approximately 2°-3° C. In oneimplementation, the actual gas temperature can be sent from the blendercontroller 60 via communication bus 38 to the processor 26 of theadaptive controller 18 to be displayed on, e.g., a three digit displayforming a part of the user interface 30. In other embodiments, a displayforming a part of user interface 30 can be realized as a touch screendisplay or other display that is utilized to display any desired set ofoperational parameters of the system and measurements from the patient.Further, the user interface 30 may include virtual and/or actual buttonsand indicators as well as other controls for use by medical personnel toenter data and provide directives for prescribed delivery of therapeuticgas blends for inspiration by the patient 10, setting alarm limits, etc.

The system 34 may also provide for measurement of at gas flow rateand/or pressure at 80 with such measurement being provided to andcontrolled by the processor 60. Processor 60 can further provide thepressure and/or flow rate information as well as other operationalparameters and alarms via bus 38 to processor 26 for display to medicalpersonnel on user interface 30. Control of the flow rate and pressure ofthe gases can be implemented by controller 60 by use of valves at theoxygen mixer 64 (or elsewhere). Additionally, the processors 60 and 30can compare various measured data with a set of prescribed alarm limits(either pre-configured or set by input by medical personnel) which willcause alarms to be generated (i.e., audible and visual alarms, orsignals that can be monitored remotely—such as at a nurse's station),shown as 84.

Hence, the present adaptive controller system 18 uses input signals of apatient's blood oxygen levels, as assessed by the pulse oximeter, tocalculate the appropriate oxygen level for delivery to the patient bythe blender system 34. The adaptive controller processor 26 continuouslymonitors the patient's blood oxygen and provides oxygen level adjustmentat regular intervals, e.g., approximately every 10 seconds. PID controlis used in this example embodiment as a mechanism to adaptively adjustthe oxygen levels to the needs of the patient as assessed by the pulseoximeter.

In the present system, under most conditions, the overall system controlis handled by controller 26 operating as a master controller. However,the delivery of gasses to the patient can be controlled by either theadaptive controller system in an adaptive mode or can be overridden by amanual mode implemented by control of either the adaptive controllersystem 18 or by the blender system 34. For example, at times, theblender system 34 send signals to the adaptive controller system 18directing an operational mode change, such as from automatic to manualadjustment of oxygen levels. So, for example, if medical personnel takean action at the blender system 34 to take over control of the gas blendor other operation of the blender system manually, the blendercontroller 60 detects this action and instructs the processor 26 torelinquish control over the gas mixture to a manual override controlledat the blender system.

In accord with the present teachings, processor 26 may be one or moreprogrammed processors programmed in any one or more suitable languagessuch as C, C++, Perl, etc., as well as other adjunct languages wheredesirable. The processor 26 can be implemented using, for example,industry standard processors such as the Atmel ARM-based processors suchas the SAM9263 series microcontroller (e.g., the AT91SAM92638) runningthe GNU/Linux operating system. The above constraints are not to beconsidered limiting since other configurations can also be utilized.

In systems consistent with the present teachings, certain defaultsettings can be provided to establish a baseline operation in theabsence of overriding instructions from medical personnel. Such defaultsettings can be stored at 28. In one example embodiment, theillustrative non-limiting default settings of TABLE 1 can beestablished.

TABLE 1 Parameter Default Value Pause time 1 minute Default pulseoximeter cable connection type Masimo ™ Default operational mode ofBlender System Blend Mode Default O₂ mixture for delivery to patient 35%Default airway connection Nasal Cannula O₂ Maximum Alarm 60% O₂ MinimumAlarm 21% O₂ Limit Alarm 60% Pulse Rate Minimum Alarm 80 bpm Pulse RateMaximum Alarm 180 bpm

BLEND MODE/SMART MODE (AND OTHER MODES)—There are two (2) modes ofoperation in the present implementation: BLEND and SMART. Blend mode is“manual” mode of operation where the end-user makes manual adjustmentsof oxygen percentage. Smart mode is where the computer makes adaptiveadjustments of oxygen percentage. Other modes of operation may bedevised without limitation

Possible airway connection settings Nasal cannula. The default settingfor airway connector is NASAL CANNULA. Other options of airwayconnectors include MASK in which a mask is used. When used with invasivesystems or other airway connectors, other connection settings can beprovided for.

O₂ max and min—The preset values of oxygen limits are about 21% andabout 60%. The lowest value is about 21% but the upper value can be setas high as about 80% in this implementation.

Pulse rate max and min—The preset values of pulse rate are about 80 bpmand about 180 bpm in this implementation. These values can be adjust upof down by the end-user.

Upper O₂ limit—This LIMIT is a safety feature of the device. The presetlimit is about 60% O₂ in the present embodiment and can be adjusted bythe end-user. The O₂ Maximum Alarm can be set above or below this LIMIT.

Other alarm limits can also be established such as interface type, flowrate, temperature, humidity, manual override status, etc.

In this example, the pause time is the default amount of time that themicroprocessor uses to indicate an internal problem or fault that isdetected at startup and during operation. The Pause Time is the timeused by a watchdog timer to determine that the system has locked upduring boot or has otherwise malfunctioned during operation (e.g., stuckin a loop or other error has occurred that interferes with normal systemoperation). When this pause time expires it is indicative that thesystem has detected a failure and a critical alarm is issued.

The Operational mode of the blender system can be Blend Mode in whichthe air and oxygen are blended. 100% oxygen is delivered and mixed withabout 21% Air. The default O₂ mixture of about 35% is the defaultsetting in certain embodiments for the blender to produce in the absenceof another setting. The default airway connection is Nasal Cannula,which the user can override with settings such as Mask or Endotracheal.The O₂ maximum alarm limit sets an alarm when the O₂ level beingdelivered exceeds a defined limit. The O₂ minimum alarm limit sets analarm when the O₂ level falls below a prescribed limit. The Upper O₂alarm limit is a safety feature to ensure that oxygen does not riseabove the preset value of 60%. The minimum and maximum pulse limitsdefine a range of pulse rates allowable with an alarm being produced ifthose minimum and maximum values are breeched.

Alarm 34 may provide any of several alarm conditions, as will beexplained later. Briefly, a cautionary audible alarm signal may include(e.g., an audible tone, beep, buzz, voice or the like). In one exampleembodiment, the processor 26 controls the alarm to produce an audiblesignal with a sound pressure level that is within, for example, about±0.3 dB of an Emergency Alarm Audible Tone measured at the point ofabout 1 meter from the user interface of adaptive controller system 18.The Emergency Alarm Audible Tone, is similarly controlled by theprocessor 26 to produce an output audible alarm signal that has a soundpressure level of 70 dB±10 dB measured at the point of about 1 meterfrom the adaptive controller system 18.

In certain example embodiments, the user interface 30 provides for inputof data that can be stored at 28 including, for example the data shownin TABLE 2.

TABLE 2 INPUT FUNCTION Power Button This button is used to turns theAdaptive Controller System on and off StandBy Button Puts the AdaptiveController System into manual adjustment mode Smart Button Puts theAdaptive Controller System into computer adjustment mode Initial O₂Button Sets initial O₂ level - overrides default O₂ Upper Limit ButtonSet upper limit of O₂ level - overrides default SpO₂ Upper Alarm Setupper SpO₂ alarm - overrides default SpO₂ Lower Alarm Sets lower SpO₂alarm - overrides default Pulse Rate Upper Alarm Set upper pulse ratealarm - overrides default Pulse rate Lower Alarm Sets lower pulse ratealarm - overrides default Trend Time Used to set a Trend Time framewhich provides a graphical representation of alarms, alarm conditions,O₂ level, SpO₂, oxygen delivered, pulse rate, etc. O2 Increase ButtonIncrementally increase O₂ level O2 Decrease Button Incrementallydecrease O₂ level Time/Date Allows entry of a new Time or Date PatientData Allows entry of patient data

The user interface 30 can further provide display visual indicators anddata that are useful to the medical personnel in treating patient 10.Such displayed information may, for example include some or all of thedata of TABLE 3 as well as other data that may be deemed useful withoutlimitation:

TABLE 3 DISPLAY FUNCTION Power Button Indicator Indicates position andavailability of Power Button (note - not always available for safetyconsiderations) Operational Mode Indicates mode of delivery of gas O₂display Indicator of O₂ level delivered by Blender system SpO₂ DisplayIndicator of SpO₂ level assessed by pulse oximeter Pulse Rate DisplayIndicator of pulse rate level assessed by pulse oximeter StandBy DisplayIndicates if Adaptive Controller System is in manual mode Smart DisplayIndicates if Adaptive Controller System is in in computer mode TrendTime Indicates trend time-frame O₂ Upper Limit Alarm Indicates when O₂exceeds upper limit SpO₂ Alarm Indicates when SpO₂ has exceeded upper orlower limits Pulse Rate Alarm Indicated when pulse rate has exceededupper or lower limits Low Perfusion Alarm Indicated when SpO₂ value isnot reliable Sensor Off Patient Alarm Indicated when SpO₂ sensordisconnects from patient Sensor Disconnect Alarm Indicated when SpO₂sensor disconnects from Adaptive Controller System Patient Data Name andother identifiers for patient Gas Temperature Indicates Temperature ofinspired gas (from Blender System) Gas Humidity Indicates Humidity ofinspired gas (from Blender System) Gas Flow Rate Indicates flow rate ofinspired gas (from Blender System)

FIG. 2 depicts one simplified non-limiting example of a collection ofdata displayed in an illustrative user interface display 30.

FIG. 3 shows one non-limiting example of a PID controller 120 as can beimplemented in processor 26 and used in certain implementations tocontrol oxygen mixer 64. In other example implementations, a PIcontroller (Proportional Integral) or other suitable feedback controllercould alternatively be used. The proportional-integral-derivativecontroller (PID controller) 120 is a control loop feedback controllerthat calculates an error value as the difference between a measuredprocess variable and a desired value of the process variable (or setpoint). The controller operates to minimize the difference between ameasured value and the set point. A PID controller accomplishes this byuse of an algorithm that uses three separate parameters—proportional(P), integral (I) and derivative (D) values interpreted at discreteincrements of time where P depends on the current error, I depends ofthe accumulation of past errors, and D predicts future errors. Theweighted sum of these three actions may be used to adjust a process—inthis case the proportion of oxygen represented FiO₂.

In FIG. 3, when a conventional PID controller is used and when all threefunctions P 122, I 124 and D 126 are utilized, the values of P, I and Dare given by Equations 1-3.

$\begin{matrix}{P = {K_{p}{e(t)}}} & \left( {{Equation}.\mspace{14mu} 1} \right) \\{I = {K_{i}{\int_{0}^{t}{{e(\tau)}d\;\tau}}}} & \left( {{Equation}.\mspace{14mu} 2} \right) \\{D = {K_{d}\frac{{de}(t)}{dt}}} & \left( {{Equation}.\mspace{14mu} 3} \right)\end{matrix}$

The oxygen mixer control signal is derived from the PID controlleroutput from adder 130 and is represented as u_(t) in Equation 4.

$\begin{matrix}{u_{t} = {{P + I + D} = {{K_{p}{e(t)}} + {K_{i}{\int_{0}^{t}{{e(t)}{dt}}}} + {K_{d}\frac{{de}(t)}{dt}}}}} & \left( {{Equation}.\mspace{14mu} 4} \right)\end{matrix}$

Components of Equation 4 are defined as follow:

K_(P: Proportional gain coefficient;)

K_(i: Integral gain coefficient;)

K_(d: Derivative gain coefficient;)

e: Error, difference between measured and target;

t: Time; and

: Integration variable; takes on values from time 0 to present time

.

The current value of PaO₂ (representing the measured SpO₂ as will bediscussed later) is subtracted from the setpoint (i.e., the targetvalue) at 118 to produce the error signal e at the output of 118. Thiserror signal is then processed by the P, I and D blocks 122, 124 and 126respectively according to the equations above. The outputs of blocks122, 124 and 126 are summed at 130 to produce u_(t) which is provided tothe oxygen mixer control 132. The value control signal is put into anappropriate format by oxygen mixer control 132 of processor 26 andoutput to the blender controller 60 of blender system 34. Thisinformation may then be used by the blender controller 60 to effectcontrol of the oxygen mixer 64 to establish the appropriate blend ofgasses dictated by the PID controller.

For the present embodiment, the PID controller equation is defined asEquation 5:

PaO ₂=(KL*FiO ₂)+K2,   (Equation. 5)

KL is the lung function gain coefficient relating the lung's ability toefficiently transfer oxygen and carbon dioxide. K2 is the offsetrelating to level of over-all respiratory capability.

This equation is based upon a PID controller equation from Sano andKikuchi, IEE Proceedings, Vol. 132, Pt. D, No. 5, September 1985 whichis hereby incorporated by reference and which had an offset (K2). Thisoffset has been found to be approximately zero and is negligible in thepresent embodiment. Hence, K2 has been dropped due to the system workingon the dissociation curve greater than about 85%. Accordingly, thisequation has been modified for the present application by dropping theconstant K2 for use with the present PID controller. Also, this PIDcontroller uses a relatively long sample period of about 10 secondswhich serves as a type of low-pass filter to ensure accuracy ofcalculated from the SpO₂ monitor.

Another type of low-pass filter can be provided by using, for example,about 90% of old data (from prior sample period) and adding in, forexample, about 10% of the new data (from new sample period). Both ofthese filters enhance the system performance so it is more responsivebut not overly responsive.

Another feature of the present example embodiment of the PID controlleris the “initial” value of O₂ used by the system upon initiation of theadaptive process. The initial value is set by the end-user and is usedby the PID controller to ensure the system starts in a relativelysteady-state condition. It is generally undesirable to have the PIDcontroller adjusting the O₂ level up and down upon start-up so as tofind a steady-state. The end-user's input of O₂ helps mitigate this upand down operation at startup.

It is further noted that linear interpolation of SpO₂ to PaO₂ usuallyadequately accounts for pH, Temp, and DPG. The patients using thissystem are often in managed care or in a step-down environment. Soassuming the above three (3) factors are not significant issues, pH andTemperature can be assumed to be stable. DPG is usually “washed-out” ofthe newborn's blood within 72 hours after birth.

The system is initialized to ensure that the system starts operation ina steady-state condition. An initial KL is calculated by:

KLi=PaO ₂ i/ FiO ₂ i,   (Equation. 6)

where KLi PaO₂i, and FiO₂i are all initial values.

Furthermore, within each sample period of the PID controller, anadaptation algorithm uses a calculation to form new PID gaincoefficients. The algorithm used in the present implementation is givenas:

(new) KL=0.9 (old) KL+0.1(PaO₂ /FiO ₂),   (Equation. 7)

where the (new) KL is used for calculating (new) PID gain coefficients.

In the process described above, the value of SpO₂ is measured andconverted to a value of PaO₂ for use by the PID controller for itscalculations. This conversion can be effected in a number of ways. Withreference to FIG. 4, in one example embodiment consistent with thepresent invention, the SpO₂ measurement as acquired by the pulseoximeter is converted into the correlating partial pressure of arterialoxygen (PaO₂). This is done in the present embodiment because of therelationship between PaO₂ and control of the example oxygen mixer 64,but in other embodiments control signals for the oxygen mixer can bemore directly derived from SpO₂ or other measures of a patient's bloodoxygen concentration without limitation.

Conversion from SpO₂ to PaO₂ can be accomplished in a variety of ways.Conventionally, medical personnel may utilize an oxyhemoglobindissociation curve to obtain PaO₂ from SpO₂ under standard conditions ofTemperature=37° C., pH 7.4, and BE=0. An example approximation of anoxyhemoglobin dissociation curve is shown as 150 of FIG. 4. This curveis an approximation used for illustration in this document only and isnot to be used for treatment of a patient. In this illustrative curve,if one knows the value of SpO₂, the value of PaO₂ can be read from thegraph. However, the relationship becomes somewhat difficult to interpretat high levels of SpO₂. Additionally, the curve can shift left asdepicted by dashed curve 154 or shift right as depicted by dashed curve158. Shifting of the curve to the left represents conditions causinghigh O₂ affinity. Shifting of the curve to the right representsconditions causing low O₂ affinity.

The curve 150 approximates a sigmoidal shape and various equations canbe devised to closely model the shape of the curve using various curvefitting techniques. With such an equation, the value of PaO₂ can becomputed directly. However, such computation is complex andcomputationally intensive. In certain example embodiments, data pointsfrom this curve can be cataloged into a lookup table stored in storageand/or memory 28 which can be used to convert the value of SpO₂ to avalue of PaO₂. This can be done to any desired degree of accuracy foruse as a lookup table.

Under the above standard conditions, the relationship between SpO₂ andPaO₂ can be approximated by a lookup table such as the partial lookuptable shown in TABLE 4.

TABLE 4 SpO₂ PaO₂ 10 10 30 19 40 23 50 26.5 60 32 70 37 80 44.4 81 45 8246 83 47 84 49 85 50 86 52 87 53 88 55 89 57 90 60 91 62 92 65 93 69 9473 95 79 96 86 97 96 97.5 100 98 112 99 145 99.75 150

This lookup table is again for illustrative purposes only and notintended for the treatment of any patient. In certain exampleimplementations, the above TABLE 4 (or a more complete and more precisetable) may be used to translate SpO₂ to PaO₂ by first doing a look-up ofthe value of SpO₂ and then, if the exact value is not on the table,doing a linear or non-linear interpolation or any suitable interpolation(e.g., polynomial, piecewise constant interpolation, splineinterpolation, bilinear interpolation, extrapolation, etc.). Usinglinear interpolation by way of example, if the SpO₂ value is 91.6, thePaO₂ value can approximated by using a linear interpolation to beapproximately:

PaO ₂=(91.6−91)/(92−91)×(65−62)+62=63.8   (Equation. 7)

The more data points provided in the lookup table, the more accurate aninterpolation, if necessary, will be. It is noted that the above TABLE 4is presented by way of example and is only approximately accurate understandard conditions discussed above. The example lookup table is smalland may result in undesirable accuracies, but is presented for ease ofillustration of the principals involved. It is again noted that neitherthe curves of FIG. 4 nor the data of TABLE 4 should be used for actualmedical purposes. This data is only provided for purposes ofillustration. Accurate medical references should be used for actualpatient treatment purposes.

Referring now to FIG. 5, an illustrative flow chart 100 depicting anoverall mode of operation of certain implementations is depictedstarting at 102. At 106, the system is initialized with all relevantparameters including PID controller gain coefficients, and the medicalstaff inputs type of delivery (invasive or non-invasive) along withother relevant data including patient information. At 110, the SpO₂reading is taken from the pulse oximeter and this measurement isconverted to PaO₂ at 114. A new value of KL can then be computed at 118and new PID controller gain coefficients can be calculated at 122. Thiscalculation results in determination of parameters that can be used bythe blender controller to calculate valve control parameters to obtainthe target SpO₂ as computed by the processor 26 at 126. Accordingly, thevalves of oxygen mixer 64 can be adjusted by blender controller 60 toachieve the desired gas mixture at 130.

At 134, the blender controller reads various data generated in theblender system 34 such as temperature, humidity, pressure, gas flow,etc. and sends that data to processor 26 of the adaptive controllersystem 18 via bus 38. The processor 26 then sends the data from theblender system 34 as well as internally generated data to a displayforming a part of user interface 30 for reading and interpretation bymedical personnel at 138. Processor 26 also compares the data sent bythe blender system with established default or operator set alarm limitsat 142. If any alarm limits are exceeded at 146, an alarm 84 isgenerated at 150 to alert medical personnel that there is a potentialproblem. For example, if the processor detects that the patient's SpO₂level is below a threshold (e.g., 90%), an alarm may sound to alertmedical personnel that there may be either a degradation of thepatient's condition or there may be a malfunction. In another example,if the temperature of the inspired gas mixture is detected to be greaterthan an upper limit (e.g., 40° C.), then an alert may be generated tolet the medical personnel know that there is a potential problem.

Additionally, in certain cases, where possible, the adaptive controllersystem 18 may take certain corrective actions at 156 when an alarm limitis exceeded. In one example, if the alarm limit is exceeded for thelower limit of SpO₂, the adaptive controller processor 26 may, forexample, cease to provide adaptive control over the gas mixture.Additionally, the control processor may set a prescribed or defaultoxygen mixture (e.g. 60%) or at the most recent oxygen mixture to bedelivered by the blender system 34 and revert the blender system tomanual control while sounding an audible alarm and providing a visualindication of the situation and actions taken. Other actions arepossible without departing from the present teachings.

FIG. 5 depicts a simplified example process that illustrates the overalloperation of the system 26. Referring now to FIG. 6A-6I, starting atFIG. 6A, an example process 200 is depicted for operation of theadaptive controller system as described herein in flow chart form. Theprocesses depicted are carried out in certain implementations utilizingprocessor 26 to control the adaptive controller system 18. Suchprocessor may be realized as a hard wired processor or as a programmedmicrocontroller or the like that includes or is connected tonon-transitory memory devices that store instructions that when executedon the processor 26 (which may also be realized as multiple processors)cause the processes described to be carried out. The system includesprogram memory (not shown explicitly), with unused locations of theprogram memory being set to an instruction that will cause the processorto go to a known safe state if executed.

The system 18 operates in a number of defined functional states, some ofwhich are states which are continually passed through in order to carryout certain monitoring and alarm functions. The process begins at 202after which at 206, if the system is not turned on, the only function isretention of non-volatile memory contents that stores non-volatile data.

When the system 26 is turned on at 206, a booting and initializationprocess is carried out at 214 wherein program instructions are loaded,initial checks are carried out and so forth. The power on/standby stateis entered at 218 at which point a standby button or other indicator isilluminated and a smart button (indicating operation of the system 26 inadaptive control mode) and illumination associated therewith isdisabled. This state is entered when power is first applied to thecontroller or after an emergency alarm or after a manual change inoxygen level of the blender system 34.

At 222, regardless of the state of the system 18, editing of time, date,patient data, gas mixture delivery mode, network link system tests anddownload of data to external storage or to remote monitoring stations(not shown) is permitted. At 226, the system action is determined by thestate or states that are currently active. It is noted that certainstates may be active at all times, while others are only active uponuser control or under alarm conditions, etc. However, depiction of thesystem operation as a collection of states is a convenient mechanism toconvey the operation of the present illustrative example embodiment.

When the system is in the standby state, various measurements can bedisplayed in certain implementations. With reference to FIG. 6B, whenthe standby state is entered at 230, the O₂ level and upper limit buttonare illuminated and adjustment of associated parameters is permitted.

Referring to FIG. 6C, the general operation of the system 18 when in the“smart” mode state is depicted. In this state, the system 18 isoperating to carry out adaptive control of the gas mixture produced byblender system 34 using the PID control mechanism or other suitablemechanism as describe previously. Upon entering this state at 234, thestandby, O₂ level, O₂ upper and lower limits are illuminated andenabled. Controller 26 is initially disabled while editing an entry ofpatient, time, date and other parameters are entered.

At 238, the smart control parameters are set and the smart controlenable button is illuminated and enabled. The standby button andillumination are disabled as are the manual O₂ adjustment button andillumination thereof, and the upper limit button and illuminationthereof. Smart (adaptive) control of the gas mixture is then commencedat 242 in order to utilize the SpO₂ feedback PID control of the gasmixture to achieve a target peripheral blood oxygen level as measured bythe pulse oximeter 12.

If a state change is detected at 246, and if such state change dictates,the smart mode may be exited at 250. Whenever a state change occurs thatdictates exiting the smart mode, a provision is made at 254 to continueto supply a blend of gasses to the patient 10. In the present example,the gas mixture is set at the last setting dictated by the adaptivecontrol system 18. In other examples, the O₂ level could be set foranother value including increased or decreased oxygen levels or apredefined default level without limitation. When the smart mode isexited, the medical personnel are notified by an alarm so that manualcontrol can be instituted based upon the patient's condition. At 258,the smart control parameters set at 238 are inverted and the system 18enters the standby mode at 218. Smart mode operation is not reentereduntil the medical personnel take steps to re-activate the smart mode.

There are multiple events that can trigger one or more of multiple typesof alarms depending upon the severity of the alarm condition. Theoperation of the alarms states is depicted in the example process ofFIG. 6D starting at 266 where alarm conditions are monitored and alarmconditions are detected. When an alarm is detected at 266, the type ofalarm is determined based upon the input received by the processor 26.Several examples of alarm conditions include, but are not limited to:low perfusion, pulse rate limits exceeded, sensor off patient ordisconnected, pressure loss, SpO₂ upper or lower limits exceeded, lowbattery, AC power loss, inspired gas temperature or humidity outsidelimits, flow rate limits exceeded, blender system alarms, etc. When analarm condition exists, the type and severity of the alarm aredetermined at 270.

Some alarms may be deemed by the system 18 to be issues that should bemonitored. For example, a slight deviation in gas humidity or a lowbattery when operating on AC power may not be an emergency, but shouldbe brought to the attention of the medical personnel. Other alerts suchas a loss of pulse or SpO₂ readings are deemed unreliable may be deemedan emergency condition. In any case, at 274, an audible and/or visualalarm is produced according to the type and severity of the alarm state.The types of alarm conditions will be discussed later.

At 278, if the system 18 is operating in smart mode and thus adaptivelycontrolling the gas mixture, and if the alarm is of such nature thatadaptive control is deemed inappropriate at 282, the smart mode isdisabled at 286 and the gas mixture level is set to the latest pre-alarmlevel so that medical personnel can make adjustments manually.

If the alarm is such that the adaptive control (smart mode) can bemaintained at 278, then 282 and 286 are bypassed and the smart modecontinues. From 286 (or 282 or 278 if the alarm does not interrupt smartmode operation), control passes to 288 where if the alarm state isresolved, then the audible and visual alarms are disabled at 294. If thesmart mode is still active at 298, control returns to 266 to await andmonitor for another alarm condition. If the smart mode has been disabledat 286 as determined at 298 (for example in the case of an alarmindicating that the measured oxygen levels are not reliable), then thesystem enters the standby state at 218 until operation of the adaptivecontrol is resumed under operator control.

An example manual adjustment state is depicted in FIG. 6E. In thisstate, the system is in standby mode at 302 and the standby button isilluminated. The smart mode is disabled and the O₂ enable button isenabled and illuminated. The system 16 remains in standby until suchtime as there is a state change that, for example, takes the system intosmart mode at 306. Control then passes to 226.

An example of the graphic state is depicted in FIG. 6F. In this state,the operator is able to edit graphics parameters at 312 for graphicaldata that can be displayed, stored or printed from the system 18. Anexample is a time period for the graphic display. Such graphic displaycan present trend data and other information to the medical personnelthat are indicative of the patient's progress and trends, for example.In one example, the data can represent SpO₂ over, pulse or gastemperature a selected time period. Those skilled in the art willappreciate that other graphical values can also be presented uponconsideration of the present teachings. This state is maintained untilexited at 316 by user control or, for example, by time out.

FIG. 6G represents an example of operation of system 18 in a data inputstate. In this state, the system 18 permits input at 320 of alarm limitsand other data that may set system operational parameters. This state ismaintained until exited at 324 by user control or, for example, by timeout.

FIG. 6H represents an example state of operation of system 18 in which asignal indicating that a manual override has been initiated at theblender system 34. This signal is detected by the processor 26 as aresult of a message from blender controller 60 at 330. In responsethereto, the system 18 generates a brief audible and visual alarm at 334(a cautionary alarm) and a manual override indicator is illuminated at338. The system 18 then halts adaptive control of the gas mixture at 340and enters the standby mode until the smart mode is reactivated byoperator control. Manual override may be engaged by, for example, useradjustment of a gas mixture at the blender system 34 or by a control atinterface 30. When this occurs, the occurrence of this event is conveyedfrom the blender system 34 to the adaptive controller system 18 via bus38.

System 18 may also be configured to carry out multiple system integritytests on a periodic and/or ongoing basis in order to assure properoperation of system 18. FIG. 6I depicts an example of several integritytests that may be carried out in accord with the present teachingsstarting at 340.

At 344, the system can carry out a watchdog check in which criticalareas of functionality are examined to determine if the functions areoperating as designed and as expected. A check of data memory stacks iscarried out at 348 to determine if a stack overflow or underflow hasoccurred. At 352 a check is made to determine if the system has detecteda defective pulse oximeter sensor. At 356, the system determines ifthere is a defective pulse oximeter probe or if the probe isincompatible. At 360, the system determines if an error condition ordefective operation alarm has been discovered by the blender system 34and the blender system has reported that error via 36. Other integritychecks as depicted by 364 can also be carried out. In any of the abovecases, an alarm is generated in accord with the type and severity of theerror condition at 368.

Referring to FIG. 7, an example method 400 for processing alarms isdepicted starting at 404. In this example implementation, two types ofalarms are provided for so that the alarms are classified as either“cautionary” or “emergency”. Those skilled in the art will appreciateupon consideration of the present teachings that other types of alarmsand alarm processes can be devised upon consideration of the presentteachings.

At 408 a determination is made as to the severity of the alarm. In mostinstances this may be as simple as an association between type of alarmand a designated severity. If the alarm is considered “cautionary”, inthis example a warning indicator is flashed at 412 and an audible alarmis generated. The alarm condition, time, etc. is logged to non-volatilestorage at 416. In the cautionary alarm mode according to the presentillustrative embodiment, the operator can manually mute the audiblealarm. The muting, in this embodiment may only be temporary until thealarm is cleared. Once the alarm is sounding and displaying a flashingcautionary alarm indicator, the operator can mute the alarm by operationcarried out at the user interface 30 and this condition is detected at420. Once muted, a timer is started at 424 for a specified period oftime (e.g., two minutes). The alarm condition is monitored at 428 todetermine if the alarm condition has been cleared by resolution of thecondition causing the alarm. If not cleared, the state of the timer ischecked at 432. Once the timer expires, if the alarm condition has notbeen cleared at 428 the audible alarm is unmuted at 436 and controlreturns to 420.

Once the alarm condition has been cleared, as detected at 428, theaudible alarm is unmuted and the visual indicator (flashing warningindicator) is cleared at 440 and the alarm process exits at 450. When,at 420, the alarm has not been muted, the timer operation is bypassed sothat control passes from 420 to 428 and the process loops as shown untileither the alarm is muted, or the alarm is cleared. Many variations arepossible upon considering the present teachings.

If the type of alarm is of higher severity, the present example utilizesan “emergency” alarm as detected at 408. When an emergency alarm isdetected at 408, an audible alarm which is distinctive from thecautionary alarm and a visual indication of an emergency alarm isgenerated at 454. In the present example, the alarm cannot be clearedmanually, per se, except for example by reverting the adaptivecontroller system to standby or manual control or turning off theadaptive controller system.

The alarm is logged to non-volatile storage at 458 and the processdetermines if the system is operating in the smart mode (adaptivecontrol of the blender system) at 462. If so, and the alarm is of a typethat is configured to suspend the adaptive control of delivery of theblend of gasses to the patient at 466, then adaptive control issuspended at 470 and the gas mixture from the blender is set to the mostrecently set blend of gasses and control passes to 474. At this point,the blender system can be operated manually to adjust the blend ofgasses based on the judgment of medical personnel. If, at 462, thesystem is not operating in smart mode, or if at 466, the alarm of a typethat is configured to suspend operation of the smart mode, the processalso proceeds to 474 where the system determines if the alarm conditionhas been cleared. The alarm condition remains as described until thealarm is determined to be cleared at 474, at which point, the visual andaudible alarms are cleared at 478 and the process exits at 450.

Again many variations are possible in the emergency alarm conditionincluding permitting the temporary muting of an audible alarm andclearing the alarm upon entering a manual control of the blender system.Other variations will occur to those skilled in the art uponconsideration of the present teachings.

In accord with an example embodiment, detection of low perfusion resultstransition to the emergency alarm state. This is a condition in whichthe pulse oximeter data indicates data is not reliable for use by theprocessor 26. Similarly, if the pulse oximeter detects that the sensoris off the patient or not attached, processor 26 initiates an emergencyalarm since pulse oximeter data is not reliable.

In the condition in which upper or lower SpO₂ alarm limits are exceeded,or the pulse rate upper and lower alarm limits are exceeded, theprocessor generates a cautionary alarm.

In certain embodiments, the system enters the standby state if theblender system tells the adaptive control system that an operator hasmade a manual adjustment to the blender system. In the event of apressure loss is detected by the blender system of any or all gasses, anemergency alarm is initiated by the processor 26. A cautionary alarm isgenerated if the system detects that the battery's energy level does notexceed capability to maintain the adaptive controller 18 in operationalmode for more than a designated amount of time, for example more thanabout 5 minutes, AC power support. Similarly, a cautionary alarm isgenerated if the AC power disconnect is disconnected.

The type of alarm condition (cautionary or emergency) can be determinedby the nature of the alarm that is detected. In cautionary alarms,according to an example implementation, a yellow warning indicator isilluminated and flashed.

The alarms may be logged to non-volatile memory information including,but not limited to a code corresponding to the alarm condition that wasdetected and a time representing the number of seconds since the lastpower on.

In emergency alarms, according to the present example, the alarm modecan be determined by the alarm detection function that caused the alarmto be invoked. Emergency alarms may be generated, for example, when theSpO₂ level crosses the upper or lower alarm limit. Similarly, anemergency alarm may be initiated upon detection that the pulse ratecrosses the upper or lower pulse rate alarm limit, or when low perfusionis detected, or when the sensor is detected to be off the patient ordisconnected; or when low pressure of any or all gasses is detected.Additionally, an emergency alarm may be generated if the system detectsa communication failure between the adaptive controller system 18 andthe blender system 34.

FIG. 8 depicts a block diagram illustrating a system 500 according toanother embodiment of the subject matter described herein. The system500 includes a regional oximeter 504, a regional oximeter processor 508,and an interface 512 in addition to the pulse oximeter 12, the pulseoximeter processor 22, and the interface 24 of FIG. 2 for monitoring thepatient 10. The system 500 allows cerebral tissue monitoring and controlof oxygen saturation (SpO₂) of the blood using the regional oximeter 504to prevent cerebral hypoxia. In addition, the system 500 allowsmonitoring oxygen saturation of the systemic arterial system via thepulse oximeter 12 as disclosed in FIG. 2.

The cerebral tissue monitoring of the brain arterial saturation usingthe regional oximeter 504 is different than monitoring systemic arterialsaturation using the pulse oximeter 12. Specifically, the pulse oximeter12 is configured to measure an arterial saturation range that istypically between about 85% and about 100%. However, the regionaloximeter 504 is configured to measure a cerebral arterial saturationrange that is typically between about 55% and about 75%.

The system 500 operates in a first mode utilizing the regional oximeter504, the regional oximeter processor 508, and the interface 512. Theregional oximeter 504 may be the Masimo Root® with O3® Regional Oximetrymonitor or the like. The regional oximeter 504 provides regionaloximetry SpO₂ data via the interface 512 to the regional oximeterprocessor 22. The regional oximeter processor 504 is configured toconvert the regional oximetry SpO2 data into a form best processed bythe adaptive controller 26 (e.g. programmed processor/PID controller).In certain embodiments, the regional oximeter processor 508 and theinterface 512 may be integrated within the adaptive controller 26.Overall the system 500 may be configured to operate in the first mode ina manner similar to FIG. 5 with the exception of the SpO₂ reading (step110) being taken from the regional oximeter 504. Additionally, thesystem 500 may be further configured to operate in the first mode in amanner similar to FIG. 6A-6I and FIG. 7.

The system 500 also operates in a second mode utilizing the pulseoximeter 12, the pulse oximeter processor 22, and the interface 24. Thepulse oximeter 12 may be the Masimo Radical-7® Pulse CO-Oximeter or thelike. The pulse oximeter 12 provides pulse oximetry SpO₂ data via theinterface 24 to the pulse oximeter processor 22. The pulse oximeterprocessor 22 is configured to convert the pulse oximetry SpO₂ data intoa form best processed by the adaptive controller 26. In certainembodiments, the pulse oximeter processor 22 and the interface 24 may beintegrated within the adaptive controller 26. Overall the system 500 maybe configured to operate in the second mode in a manner similar to FIG.5, FIG. 6A-6I, and FIG. 7.

The system 500 also includes a software switch which allows a user fromthe GUI 30 to select either the first mode or second mode of operationfor the system 500. Additionally, the system 500 may be configured toautomatically switch from the first mode to the second mode when SpO₂data from the regional oximeter 504 is determined to be invalid and SpO₂data from the pulse oximeter 12 is determined to be valid. The system500 may also be configured to automatically switch from the second modeto the first mode when SpO₂ data from the pulse oximeter 12 isdetermined to be invalid and SpO₂ data from the regional oximeter 504 isdetermined to be valid.

In some embodiments, the GUI 30 may be configured to display both anSpO₂ value from the regional oximeter 504 and an SpO₂ value from thepulse oximeter 12 whether in the first mode of operation or in thesecond mode of operation. In other embodiments, the GUI may only displaythe SpO₂ value from the regional oximeter 504 in the first mode ofoperation and the GUI may only display the SpO₂ value from the pulseoximeter 12 in the second mode of operation.

In the first mode of operation, the system 500 uses a first sigmoidshaped oxyhemoglobin dissociation curve cataloged into a first lookuptable stored in storage and/or the memory 28 to convert the value ofSpO₂ received from the regional oximeter 504 to a value of PaO₂. Incertain example implementations, TABLE 5 (or a more complete and moreprecise table) may be used to translate SpO₂ to PaO₂ by first doing alook-up of the value of SpO₂ and then, if the exact value is not in thetable, doing a linear or non-linear interpolation or any suitableinterpolation (e.g., polynomial, piecewise constant interpolation,spline interpolation, bilinear interpolation, extrapolation, etc.). ThePaO₂ value is then used to determine a gas mixture for the first mode ofoperation. As with TABLE 4, TABLE 5 is also for illustrative purposesonly and is not intended for the treatment of any patient.

TABLE 5 SpO₂ PaO₂ 10 10 20 19 30 23 35 26.5 40 32 45 37 50 44.4 51 45 5246 53 47 54 49 55 50 56.5 52 58 53 59.5 55 61 57 62.5 60 64 62 65.5 6567 69 68.5 73 70 79 71.5 86 72.5 96 73 100 73.5 112 74 145 75 150

In the second mode of operation, the system 500 uses a second sigmoidshaped oxyhemoglobin dissociation curve cataloged into a second lookuptable stored in storage and/or memory 28 to convert the value of SpO₂received from the pulse oximeter 12 to a value of PaO₂. In certainexample implementations, previously disclosed TABLE 4 (or a morecomplete and more precise table) may be used to translate SpO₂ to PaO₂by first doing a look-up of the value of SpO₂ and then, if the exactvalue is not in the table, doing a linear or non-linear interpolation orany suitable interpolation (e.g., polynomial, piecewise constantinterpolation, spline interpolation, bilinear interpolation,extrapolation, etc.). The PaO₂ value is then used to determine a gasmixture for the second mode of operation.

The clinical application of the system 500 includes heart attack andstroke patients (and possibly with new born infants suffering severebrain hypoxia) who have the potential for brain cell damage due to highoxygen levels within the brain. As such, system 500 monitors andregulates the oxygen levels in the brain so as to potentially reducetrauma to the brain due to excessively high oxygen levels that are aresult of current oxygen therapy techniques.

In some embodiments, the system 500 may omit the pulse oximeter 12, thepulse oximeter processor 22, and the interface 24. As such, the system500 is then configured to operate only in the first mode and the secondlookup table (e.g. TABLE 4) is not needed. Additionally, the regionaloximeter 504 may be configured to monitor other tissue oxygenationlevels for organs such as a kidney or gut.

Many variations will occur to those skilled in the art uponconsideration of the present teachings.

Certain example embodiments described herein, are or may be implementedusing a programmed processor executing programming instructions that arebroadly described above in flow chart form that can be stored on anysuitable electronic or computer readable non-transitory storage medium(such as, for example, disc storage, Read Only Memory (ROM) devices,Random Access Memory (RAM) devices, network memory devices, opticalstorage elements, magnetic storage elements, magneto-optical storageelements, flash memory, core memory and/or other equivalent volatile andnon-volatile storage technologies), where the term “non-transitory” isintended to exclude propagating signals but not memory that can berewritten or which loses its data when powered down. However, thoseskilled in the art will appreciate, upon consideration of the presentteaching, that the processes described above can be implemented in anynumber of variations and in many suitable programming languages withoutdeparting from embodiments of the present invention. For example, theorder of certain operations carried out can often be varied, additionaloperations can be added or operations can be deleted without departingfrom certain example embodiments of the invention. Error trapping can beadded and/or enhanced and variations can be made in user interface andinformation presentation without departing from certain exampleembodiments of the present invention. Such variations are contemplatedand considered equivalent.

While certain illustrative embodiments have been described, it isevident that many alternatives, modifications, permutations andvariations will become apparent to those skilled in the art in light ofthe foregoing description.

What is claimed is:
 1. A computer implemented method for providingadaptive control of a gas mixture for delivery to a patient via aseparate external gas blender system, the computer implemented methodcomprising: receiving first SpO₂ data from a regional oximeter via aregional oximeter interface; determining first PaO₂ data using a firstlookup table derived from a first sigmoid shaped oxyhemoglobindissociation curve; determining a first gas mixture value using thefirst PaO₂ data; and transmitting first adaptive feedback control dataincluding the first gas mixture value to the separate external gasblender system via a gas blender interface.
 2. The computer implementedmethod of claim 1 further comprising: receiving second SpO₂ data from apulse oximeter via a pulse oximeter interface; determining second PaO₂data using a second lookup table derived from a second sigmoid shapedoxyhemoglobin dissociation curve; determining a second gas mixture valueusing the second PaO₂ data; and upon activation of a software switch,transmitting second adaptive feedback control data including the secondgas mixture value to the separate external gas blender system via thegas blender interface.
 3. The computer implemented method of claim 2,wherein the activation of the software switch is a controlled by a userinterface.
 4. The computer implemented method of claim 3 furthercomprising transmitting at least a portion of the first SpO₂ data and atleast a portion of the second SpO₂ data to the user interface.
 5. Thecomputer implemented method of claim 4 further comprising transmittingat least a portion of the first PaO₂ data and at least a portion of thesecond PaO₂ data to the user interface.
 6. The computer implementedmethod of claim 2, wherein the activation of the software switch iscontrolled by detecting invalid data or missing data from the regionaloximeter interface.
 7. The computer implemented method of claim 1,wherein the regional oximeter is a regional cerebral oxygen saturationmonitor.
 8. The computer implemented method of claim 1 furthercomprising converting a first SpO₂ value from the first SpO₂ data to afirst PaO₂ value using interpolation upon determining the first SpO₂value is not present in the first lookup table.
 9. The computerimplemented method of claim 1, wherein: determining the first gasmixture value using the first PaO₂ data comprises determining a weightedaverage of a first sample period and a second sample period; and thesecond sample period occurs immediately after the first sample period.10. The computer implemented method of claim 9, wherein the weightedaverage is approximately 90% for the first sample period and isapproximately 10% for the second sample period of the first PaO₂ data.11. A computing device for providing adaptive control of a gas mixturefor delivery to a patient via a separate external gas blender system,the computing device comprising: a memory; and at least one processorconfigured for: receiving first SpO₂ data from a regional oximeter via aregional oximeter interface; determining first PaO₂ data using a firstlookup table derived from a first sigmoid shaped oxyhemoglobindissociation curve; determining a first gas mixture value using thefirst PaO₂ data; and transmitting first adaptive feedback control dataincluding the first gas mixture value to the separate external gasblender system via a gas blender interface.
 12. The computing device ofclaim 11, wherein the at least one processor is further configured for:receiving second SpO₂ data from a pulse oximeter via a pulse oximeterinterface; determining second PaO₂ data using a second lookup tablederived from a second sigmoid shaped oxyhemoglobin dissociation curve;determining a second gas mixture value using the second PaO₂ data; andupon activation of a software switch, transmitting second adaptivefeedback control data including the second gas mixture value to theseparate external gas blender system via the gas blender interface. 13.The computing device of claim 12, wherein the activation of the softwareswitch is a controlled by a user interface.
 14. The computing device ofclaim 13, wherein the at least one processor is further configured fortransmitting at least a portion of the first SpO₂ data and at least aportion of the second SpO₂ data to the user interface.
 15. The computingdevice of claim 14, wherein the at least one processor is furtherconfigured for transmitting at least a portion of the first PaO₂ dataand at least a portion of the second PaO₂ data to the user interface.16. The computing device of claim 12, wherein the activation of thesoftware switch is controlled by detecting invalid data or missing datafrom the regional oximeter interface.
 17. The computing device of claim11, wherein the regional oximeter is a regional cerebral oxygensaturation monitor.
 18. The computing device of claim 11, wherein the atleast one processor is further configured for converting a first SpO₂value from the first SpO₂ data to a first PaO₂ value using interpolationupon determining the first SpO₂ value is not present in the first lookuptable.
 19. The computing device of claim 11, wherein: determining thefirst gas mixture value using the first PaO₂ data comprises determininga weighted average of a first sample period and a second sample period;and the second sample period occurs immediately after the first sampleperiod.
 20. A non-transitory computer-readable storage medium, storingone or more programs for execution by one or more processors of acomputing device, the one or more programs including instructions for:receiving first SpO₂ data from a regional oximeter via a regionaloximeter interface; determining first PaO₂ data using a first lookuptable derived from a first sigmoid shaped oxyhemoglobin dissociationcurve; determining a first gas mixture value using the first PaO₂ data;and transmitting first adaptive feedback control data including thefirst gas mixture value to the separate external gas blender system viaa gas blender interface.